config: demote *Environment to interface

In order to support lazily loading the values stored in a user's `.gitconfig`,
we must wait until calling `*config.Configuration.loadGitConfig()` until it is
_absolutely necessary_.

To accomplish this, it was proposed that we introduce a wrapped variant of the
`*Environment` type, only for interacting with the `GitFetcher` that was
capable of supporting such beahvior.

As such, a new implementation of the `Environment` type must be defined. Since
previously there only existed the concrete type `*Environment`, this commit
demotes that down to `*enviornment`, and introduces the interface
`Environment`, which it implements.

config/config.go

@@ -50,14 +50,13 @@ type Configuration struct {
 	// Os provides a `*Environment` used to access to the system's
 	// environment through os.Getenv. It is the point of entry for all
 	// system environment configuration.
-	Os *Environment
+	Os Environment
 
 	// Git provides a `*Environment` used to access to the various levels of
 	// `.gitconfig`'s. It is the point of entry for all Git environment
 	// configuration.
-	Git *Environment
+	Git Environment
 
-	//
 	gitConfig map[string]string
 
 	CurrentRemote   string
@@ -187,7 +186,7 @@ func (c *Configuration) Unmarshal(v interface{}) error {
 // both is not.
 //
 // If neither field was found, then a nil environment will be returned.
-func (c *Configuration) parseTag(tag reflect.StructTag) (key string, env *Environment, err error) {
+func (c *Configuration) parseTag(tag reflect.StructTag) (key string, env Environment, err error) {
 	git, os := tag.Get("git"), tag.Get("os")
 
 	if len(git) != 0 && len(os) != 0 {

config/environment.go

@@ -11,33 +11,50 @@ import (
 // `Environment`s are the primary way to communicate with various configuration
 // sources, such as the OS environment variables, the `.gitconfig`, and even
 // `map[string]string`s.
-type Environment struct {
-	// Fetcher is the `Environment`'s source of data.
+type Environment interface {
+	// Get is shorthand for calling `e.Fetcher.Get(key)`.
+	Get(key string) (val string, ok bool)
+
+	// Bool returns the boolean state associated with a given key, or the
+	// value "def", if no value was associated.
+	//
+	// The "boolean state associated with a given key" is defined as the
+	// case-insensitive string comparison with the following:
+	//
+	// 1) true if...
+	//   "true", "1", "on", "yes", or "t"
+	// 2) false if...
+	//   "false", "0", "off", "no", "f", or otherwise.
+	Bool(key string, def bool) (val bool)
+
+	// Int returns the int value associated with a given key, or the value
+	// "def", if no value was associated.
+	//
+	// To convert from a the string value attached to a given key,
+	// `strconv.Atoi(val)` is called. If `Atoi` returned a non-nil error,
+	// then the value "def" will be returned instead.
+	//
+	// Otherwise, if the value was converted `string -> int` successfully,
+	// then it will be returned wholesale.
+	Int(key string, def int) (val int)
+}
+
+type environment struct {
+	// Fetcher is the `environment`'s source of data.
 	Fetcher Fetcher
 }
 
-// EnvironmentOf creates a new `*Environment` initialized with the givne
+// EnvironmentOf creates a new `Environment` initialized with the givne
 // `Fetcher`, "f".
-func EnvironmentOf(f Fetcher) *Environment {
-	return &Environment{f}
+func EnvironmentOf(f Fetcher) Environment {
+	return &environment{f}
 }
 
-// Get is shorthand for calling `e.Fetcher.Get(key)`.
-func (e *Environment) Get(key string) (val string, ok bool) {
+func (e *environment) Get(key string) (val string, ok bool) {
 	return e.Fetcher.Get(key)
 }
 
-// Bool returns the boolean state associated with a given key, or the value
-// "def", if no value was associated.
-//
-// The "boolean state associated with a given key" is defined as the
-// case-insensitive string comparison with the following:
-//
-// 1) true if...
-//   "true", "1", "on", "yes", or "t"
-// 2) false if...
-//   "false", "0", "off", "no", "f", or otherwise.
-func (e *Environment) Bool(key string, def bool) (val bool) {
+func (e *environment) Bool(key string, def bool) (val bool) {
 	s, _ := e.Fetcher.Get(key)
 	if len(s) == 0 {
 		return def
@@ -53,16 +70,7 @@ func (e *Environment) Bool(key string, def bool) (val bool) {
 	}
 }
 
-// Int returns the int value associated with a given key, or the value "def",
-// if no value was associated.
-//
-// To convert from a the string value attached to a given key,
-// `strconv.Atoi(val)` is called. If `Atoi` returned a non-nil error, then the
-// value "def" will be returned instead.
-//
-// Otherwise, if the value was converted `string -> int` successfully, then it
-// will be returned wholesale.
-func (e *Environment) Int(key string, def int) (val int) {
+func (e *environment) Int(key string, def int) (val int) {
 	s, _ := e.Fetcher.Get(key)
 	if len(s) == 0 {
 		return def

config/environment_test.go

@@ -7,13 +7,6 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestEnvironmentOfReturnsCorrectlyInitializedEnvironment(t *testing.T) {
-	fetcher := MapFetcher(map[string]string{})
-	env := EnvironmentOf(fetcher)
-
-	assert.Equal(t, fetcher, env.Fetcher)
-}
-
 func TestEnvironmentGetDelegatesToFetcher(t *testing.T) {
 	fetcher := MapFetcher(map[string]string{
 		"foo": "bar",
@@ -68,18 +61,18 @@ type EnvironmentConversionTestCase struct {
 	Val      string
 	Expected interface{}
 
-	GotFn func(env *Environment, key string) interface{}
+	GotFn func(env Environment, key string) interface{}
 }
 
 var (
-	GetBoolDefault = func(def bool) func(e *Environment, key string) interface{} {
-		return func(e *Environment, key string) interface{} {
+	GetBoolDefault = func(def bool) func(e Environment, key string) interface{} {
+		return func(e Environment, key string) interface{} {
 			return e.Bool(key, def)
 		}
 	}
 
-	GetIntDefault = func(def int) func(e *Environment, key string) interface{} {
-		return func(e *Environment, key string) interface{} {
+	GetIntDefault = func(def int) func(e Environment, key string) interface{} {
+		return func(e Environment, key string) interface{} {
 			return e.Int(key, def)
 		}
 	}